The present application relates generally to techniques involving production and use of articles and systems, such as to obtain information about analytes in fluids. More specifically it is directed to techniques which can provide specificity in measurements of concentration of a target analyte, such as glucose, in bodily fluids, including techniques involving production and use of implantable articles and systems.
Various implantable devices have been proposed. For example, implantable devices for monitoring glucose that are based on electrochemical sensors and glucose oxidase enzymatic reaction are available. These devices have the disadvantages that they produce the cytotoxic byproduct H2O2, they require the glucose oxidase to remain active, and they require electrical current to complete the electrochemical circuit. It would be desirable to have a device that does not have these disadvantages.
Another example of an implantable device is given in U.S. Pat. No. 6,952,603, which describes an implantable optical sensing element with a body and with a membrane mounted on the body, defining a cavity. This device is based on physical sensing rather than electrochemical sensing. The membrane is permeable to an analyte while impermeable to background species. A refractive index (RI) element is positioned in the cavity. A light source transmits light of a first intensity onto the refractive element, and a light detector receives light of a second intensity that is reflected/transmitted from/through the cavity. A controller device coupled to the detector compares the first and second light intensities and relates them to the refractive index, which in turn is related to analyte concentration. For the device to function properly, the membrane needs to be impermeable to background species because those species can alter the refractive index. Although filters can readily prevent passage of some background compounds, there are others that are more difficult to block. For example, it would be difficult to design a filter to block small uncharged molecules with molecular weight between about 50 and 500 Da while letting an analyte of similar size, e.g. glucose, through. It would be desirable to have a non-electrochemical device that has improved specificity for the analyte of interest.
More generally, it would be advantageous to have improved techniques for implantable articles and systems, including improved techniques for providing specificity for a target analyte.